Field of the Invention
A power conversion technique is provided, and more particularly about a power conversion apparatus and a control method thereof which are able to suppress inrush current.
Description of Related Art
For an electronic apparatus (such as a desktop personal computer and a notebook personal computer) to operate normally, a power conversion apparatus is usually adopted to rectify and filter an AC power to provide a stable DC power for use by the electronic apparatus. An ordinary power conversion apparatus may be composed simply of a full-bridge rectifier and a capacitor having a large capacitance. Therein, the full-bridge rectifier is used for rectifying the received AC power and outputting a DC signal; in addition, the capacitor having the large capacitance is used for filtering the DC signal to provide a stable output voltage for use by a backend circuit or a backend electronic apparatus.
In the structure of the power conversion apparatus, generation of “inrush current” is an issue that has to be overcome. More specifically, at an initial operation of the power conversion apparatus, since the capacitor having the large capacitance has not been charged yet, it is very likely that inrush current will be generated at the moment when the circuit is turned on upon receipt of the AC power by the full-bridge rectifier. Once the energy of the inrush current is too high, serious electromagnetic interference (EMI) occurs and thereby leads to difficulty for the power conversion apparatus to satisfy the standards of safety requirements. It may also be possible that the EMI damages the backend circuit and backend electronic apparatus and/or internal components of the power conversion apparatus.
In view of the above, to suppress the inrush current effectively, a thermal resistor having a Negative Temperature Coefficient (NTC) is usually connected between the full-bridge rectifier and the capacitor having the large capacitance in current power conversion apparatus so as to suppress the inrush current. Therein, the selected thermal resistor needs a relatively higher equivalent high impedance value at a low temperature, so as to dissipate energy of the inrush current. However, power consumption of the power conversion apparatus will be too high with respect to such a solution, and the performance of the power conversion apparatus is thereby reduced.